Electronic devices, such as flat panel displays and integrated circuits, commonly are fabricated by a series of deposition process steps in which layers are deposited on a workpiece and etch process steps in which the deposited material is etched into desired patterns. Such processes generally are performed within a vacuum chamber.
Commonly, the chemical reagents for a deposition or etch process comprise one or more gases, collectively called the process gas, that are dispensed into the vacuum chamber through a showerhead positioned directly above the workpiece. The process gas is dispensed through hundreds or thousands of orifices distributed across the surface of the showerhead so as to produce a desired spatial distribution of the process gas adjacent the workpiece.
In a plasma process, the showerhead also may be electrically connected to an RF power supply so as to function as an electrode. In this case, a reliable low impedance electrical connection must be provided between the showerhead and the RF power supply.
Such an RF-powered showerhead is described in commonly assigned U.S. Pat. No. 4,854,263 issued Aug. 8, 1989 to Chang et al.
Typically, the workpiece is substantially flat, and the showerhead has a surface facing the workpiece (referred to herein as the “front surface” of the showerhead) that also is substantially flat. Alternatively, the front surface of the showerhead may have a slight convex or concave curvature intended to maximize spatial uniformity of the deposition or etch process being performed on the workpiece.
The showerhead generally will be heated by the process being performed in the vacuum chamber. In non-plasma processes, the workpiece is heated by some means such as electrical resistance heating or radiant heating, which generally produces some heat transfer to the showerhead. In plasma processes, the plasma is an additional source of heat.
Heating generally causes thermal expansion of the showerhead, which can distort the original contour (i.e., flatness or curvature) of the front surface of the showerhead. Such distortion is undesirable because it may impair the spatial uniformity of the process being performed on the workpiece.
Distortion of the flatness or curvature of the front surface of the showerhead is especially likely to occur if the perimeter of the showerhead is rigidly mounted to the wall of the vacuum chamber, as in many conventional designs. Because the perimeter is fixed, thermal expansion of the showerhead will cause the showerhead surface to bow.
One solution to this problem of distortion of the flatness or curvature of the front surface of the showerhead in response to thermal expansion is to mount the showerhead by means of a flexible sheet, as described in commonly-assigned U.S. Pat. No. 6,772,827.
A flexible sheet requires some care in handling to avoid damage to the sheet. Accordingly, there is a need for alternative designs that are easier to handle.